It is well known that a disc generally includes a label side and a data side. The label side of the disc is used to allow a user to write content of the disc thereon. The data side of the disc has a data track to allow a disc drive to write or read data. Generally, when puts the disc into the disc drive, the data side faces a pickup head of the disc drive, thus the pickup head can write data on or read data from the data track.
Lightscribe is a technology developed in recent years. For this technology, a label side of a disc is coated with a specific dye. When the label side faces a pickup head, laser lights emitted from the pickup head focus on the label side, thus generating an image on the label side. Therefore, a user can see the image on the label side to distinguish different discs.
Another image forming technology, be called as label tag technology, has been published recently. In the label tag technology, laser lights emitted from the pickup head focus on a data side of a recordable disc or a rewritable disc, thus generating an image on the data side. The image may be a text-label.
Because the lightscribe technology must use a disc having a label side coated with a specific dye, the unit price of the disc is high. Moreover, a disc drive supporting the lightscribe technology must extra set up a control circuit to generate an image on a label side of the disc. In addition, after a pickup head writes data on a data side, a user must manually reverse the disc to make the label side to face the pickup head, thus an image data can be written on the label side. However, the label tag technology can operate without using of a specific disc, which means the label tag technology can be applied to any recordable discs or any rewritable discs on the market to carry out an action of image description. At the same time, the extra control circuit in the disc drive is unnecessary and the disc is no need to be reversed. Therefore, using the label tag technology to form an image has more advantages than using the lightscribe technology.
In general, when visually observing a complete blank disc with no data thereon, a data side of the disc is a mirror surface. It is well known that a data track of the disc is a spiral track, so that when recording data, a pickup head must write user data in turn along the spiral track from an inner area to an outer area. At the same time, laser lights emitted from the pickup head decrease the reflectivity of the data track. Therefore, when visually observing, the area of the data side written with user data is a dark, non-specular surface.
Referring to FIG. 1A, FIG. 1A is a schematic view showing a user data is written on a data side of a disc 100. An inner area 102 of the disc 100 is written with user data thus becoming a non-specular surface (low reflectivity). A residual area 104 with no data is still a mirror surface (high reflectivity). Referring to FIG. 1B, a straight line is used to represent a whole spiral track, the front part 102 of the spiral track is written with user data, and the rear part 104 of the spiral track is not written with any data.
In general, a compact disc (CD) or a digital video disc (DVD) both uses sessions to divide a track of the disc. A user data written on the disc every time is put in a session. When a user repeatedly writes user data on the disc, the track will have a plurality of continuous sessions. After the user data is completely written on the disc, a residual mirror surface area on the data side can be used to carry out an action of image description. The technology applied to carry out the action of image description is the label tag technology. In the label tag technology, the area written with description data can be seen as another session which must adjacent to the user data.
Referring to FIG. 1C, FIG. 1C is a schematic view showing a pattern generated after describing an image on a data side by the label tag technology. The label tag technology can be used to carry out an action of image description on the residual blank area 104 of the data side. Of course, the action of image description also uses laser lights emitted from the pickup head to decrease the reflectivity of the track, thus the image can be observed by eyes.
Referring to FIG. 1D, a straight line is used to represent a whole spiral track, the front part 102 of the spiral track is written with user data, and the rear part 104 includes a description data 106 used to show image. Due to the specification of a disc, data must be continuously written on the disc. Therefore, shown as FIG. 1D, the description data 106 must be written adjacent to the user data area 102. In addition, after the description data 106 is written on the disc, the disc can not be used to record user data or description data again.
Obviously, the description data of the label tag technology must adjacent to the user data, which means the description data cannot be arbitrarily written on any desired radial positions, but can be written only on an area after the user data. Therefore, the flexibility of the label tag technology for CD and DVD is limited.